In recent years, with high data transmission speed which is desired for various electronic apparatuses, high-speed serial transmission, such as Peripheral Component Interconnect (PCI)-Express or Universal Serial Bus (USB) 3.0, has become widespread. In the high-speed serial transmission, a subsequent signal is changed and transmitted before the level of the signal becomes stable, in order to transmit a signal by high speed.
In contrast, on a transmission line through which a signal is propagation, reflective noise is generated in a spot at which the characteristic impedance is discontinuous. The reflective noise arrives at a reception terminal while being repeatedly reflected, thereby having a negative influence on the quality of a received signal waveform (received waveform). In addition, if a variation occurs on a relative permittivity of a substrate due to a substrate production variation, a propagation delay time (substrate delay time) of an electrical signal, which passes through a transmission line within the substrate changes for each substrate. If the propagation delay time changes, reflective noise arrival timing at the reception terminal changes, and thus a signal waveform which is received in the reception terminal changes for each substrate.
In this manner, even in a case of a substrate of the same design, reflective noise arrival timing changes due to the substrate production variation, and thus a phenomenon, in which the quality of the received waveform changes for each substrate, is generated. Specifically, if the transmission speed (transmission rate) exceeds 10 Gbps and rises to 28 Gbps or 56 Gbps, a percentage of difference of reflective noise arrival timing to a bit width increases, and thus reflective noise arrival timing largely changes, even due to slight change in the relative permittivity. For this reason, according to the reflective noise arrival timing, the degree of deterioration in a quality of the received waveform largely changes, and thus a problem of the reflective noise is revealed.
In an actual machine, it is difficult to control variation, and thus it is difficult to verify, in detail, a phenomenon which is caused by the above-described production variation, in the actual machine. Therefore, it is desired to develop a technology of verifying the quality of the received waveform based on substrate production variation using high-speed digital signal transmission simulation.
Japanese Laid-open Patent Publication No. 2004-259001 and Japanese Laid-open Patent Publication No. 2000-035984 are examples of the related art.
As described above, the degree to which the substrate production variation influences the quality of the signal waveform is based on the reflective noise arrival timing. For this reason, the degree has no regularity and it is difficult to detect the worst case of the quality of the signal waveform.
Here, in a verification method in a general Printed Circuit Board (PCB) design flow, two types of analysis models are generated for a minimum value and a maximum value of a variation range of a relative permittivity of a substrate in accordance with production variation, and the signal waveform is verified using the two types of generated analysis models. Furthermore, at least one arbitrary relative permittivity (intermediate value) is manually extracted within the variation range of the relative permittivity, analysis models are generated for extracted one or more relative permittivities, and signal waveforms are verified using the one or more generated analysis models.
At this time, in a case in which a ratio of time difference (delay difference) of the reflective noise arrival timing to the bit width is low, that is, in a case in which the transmission rate is low, it is difficult for a problem of the reflective noise to occur, even when the above-described analysis method is used, and thus the influence of time difference of the reflective noise arrival timing may not be considered.
However, if the transmission rate is high, the shape of the signal waveform largely changes even due to slight delay difference, and thus there is a large influence on the quality of the signal waveform. For this reason, it is desirable to perform design by taking the substrate production variation into consideration. However, when the verification target case is manually extracted, the omission of verification of a malfunction case occurs, and thus there is a possibility that failures occur in the actual machine. In addition, even though the number of cases which are extracted within the variation range increases, there is a case in which it is difficult to avoid verification omission in a design condition such as a wiring length or a transmission speed.
According to an aspect, an object of the embodiment disclosed in the specification is to verify a deterioration case of a quality of a signal waveform caused by a substrate production variation without omission.